Narrative:

I work a night shift and when I reported to work august 2010; I was assigned to work on a cessna citation 560 ultra; along with another mechanic and a lead/authorized inspector (ai). The aircraft had been in the hangar for several days but it was my first day to work on it. From the turnover I received from the previous shift and my other coworkers who had also been working on that aircraft; the rudder trim had failed a travel check that was part of the routine check. Specifically; the rudder trim was traveling more in one direction than the other. I was also informed that the rudder trim actuator had been replaced and signed off. Since the person who replaced the actuator was working with me that day; I felt that continuing from where the job was stopped was reasonable and did not check the installation of the actuator; and the [trim] cables were [already] installed; and the writeup I was working on was to rig and tension the cables and perform the travel check. I started by attempting to center the trim tab control chain on the sprocket in the cockpit which did not improve the failure sufficiently. Therefore I thought the same could be done at the trim tab actuator which has a similar chain/sprocket system which was not centered. My colleague who also installed the actuator; decided to do that and accomplished the task. I tensioned the cables and performed the travel check which was within limits. During the travel checking process; I was in the cockpit moving the control wheel while the lead/ai and the other mechanic working with me were at the tail measuring the travel and giving me orders to move the wheel to 'nose left' and 'nose right'. I signed off the write-up; since I did the tensioning of the cable and was involved in the travel check as well. Once all maintenance was complete; the aircraft was released for an operational test flight which is a standard practice when flight control surfaces are affected. More than a month later; I was informed this morning that the trim tab control cables were found cross-installed and the trim tab was found to travel in the opposite direction from what is commanded by the turning of the trim tab control wheel. While I am glad that no accident was caused by it; I am also shocked that the error occurred and it was not caught earlier. What I believe happened is; during the travel check; when my co-worker and the lead/ai told me; by means of the two way radio we used for communicating; to turn the wheel to 'nose right'; the trim tab was also turning right and that created a 'false agreement'.complacency might have played a role in that while I was just turning the [rudder trim] wheel left and right; I did not have the maintenance manual physically with me and I was just turning the [trim] wheel. The fact that trim tabs move in opposite direction was missed; although that was clearly stated in the maintenance manual. I believe the error could have been avoided if we both had the copy of the maintenance manual and if we were reiterating the steps as we performed the travel check. Another point that could have helped capture the error early is a quick check of the installation of the cables even if the task was complete and signed. I have learned a great deal from this and will share the lesson to my co-workers. This report is prepared to notify my involvement in a maintenance activity that was not accomplished correctly; with no intent to do so; and to share lessons learned by using the provisions of the NASA aircraft safety reporting system.

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Original NASA ASRS Text

Title: Thirty plus days after a Rudder Trim Actuator change on a Cessna Citation 560 Ultra; a Mechanic was informed the trim tab cables were found crossed and the trim tab was found to travel in the opposite direction from what was commanded when turning the trim tab wheel. Aircraft had flown 53 legs before a pilot noticed the incorrect tab movement during a preflight check.

Narrative: I work a night shift and when I reported to work August 2010; I was assigned to work on a Cessna Citation 560 Ultra; along with another Mechanic and a Lead/Authorized Inspector (AI). The aircraft had been in the hangar for several days but it was my first day to work on it. From the turnover I received from the previous shift and my other coworkers who had also been working on that aircraft; the Rudder Trim had failed a Travel Check that was part of the Routine Check. Specifically; the rudder trim was traveling more in one direction than the other. I was also informed that the Rudder Trim Actuator had been replaced and signed off. Since the person who replaced the actuator was working with me that day; I felt that continuing from where the job was stopped was reasonable and did not check the installation of the actuator; and the [trim] cables were [already] installed; and the writeup I was working on was to rig and tension the cables and perform the Travel Check. I started by attempting to center the Trim Tab control chain on the sprocket in the cockpit which did not improve the failure sufficiently. Therefore I thought the same could be done at the Trim Tab actuator which has a similar chain/sprocket system which was not centered. My colleague who also installed the actuator; decided to do that and accomplished the Task. I tensioned the cables and performed the Travel Check which was within limits. During the travel checking process; I was in the cockpit moving the control wheel while the Lead/AI and the other Mechanic working with me were at the tail measuring the travel and giving me orders to move the wheel to 'nose left' and 'nose right'. I signed off the Write-Up; since I did the tensioning of the cable and was involved in the Travel Check as well. Once all maintenance was complete; the aircraft was released for an Operational Test Flight which is a standard practice when flight control surfaces are affected. More than a month later; I was informed this morning that the Trim Tab control cables were found cross-installed and the Trim Tab was found to travel in the opposite direction from what is commanded by the turning of the Trim Tab Control Wheel. While I am glad that no accident was caused by it; I am also shocked that the error occurred and it was not caught earlier. What I believe happened is; during the Travel Check; when my co-worker and the Lead/AI told me; by means of the two way radio we used for communicating; to turn the wheel to 'nose right'; the Trim Tab was also turning right and that created a 'false agreement'.Complacency might have played a role in that while I was just turning the [Rudder Trim] wheel left and right; I did not have the Maintenance Manual physically with me and I was just turning the [Trim] wheel. The fact that trim tabs move in opposite direction was missed; although that was clearly stated in the Maintenance Manual. I believe the error could have been avoided if we both had the copy of the Maintenance Manual and if we were reiterating the steps as we performed the Travel Check. Another point that could have helped capture the error early is a quick check of the installation of the cables even if the Task was complete and signed. I have learned a great deal from this and will share the lesson to my co-workers. This report is prepared to notify my involvement in a maintenance activity that was not accomplished correctly; with no intent to do so; and to share lessons learned by using the provisions of the NASA Aircraft Safety Reporting System.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.